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\title{Simulation of restoration in IP networks using OPNET}
\author{Andrea Bozzi, Andrea Lottarini}
\begin{document}
\maketitle

\section{Introduction}
This report illustrates the results obtained in some traffic engineering scenarios modeled using OPNET modeler. 
The focus is on the IP and MPLS reliability and comparison of their recovery time.
First, we are going to the describe the working scenario, then we are going to show the results collected in these different cases.

\section{Network topology and infrastructure}
The network is composed by:

\begin{itemize}
\item eight \textbf{Juniper M10} routers
\item \textbf{100BaseT} duplex links 
\item two \textbf{Ethernet IP} workstation. 
One of the workstation produces IP traffic directed to the other. 
\end{itemize}

\begin{figure}[!htbp]
\centering
\includegraphics[width=\textwidth]{./figures/setup.pdf} 
\caption{Our network topology}
\label{fig:network_topology}
\end{figure}
As we can see from Figure \ref{fig:network_topology}, each workstation is connected to only one router, while the routers can have two or three active interfaces.
The packet size is fixed among all scenarios; we chose a value of 1200 bytes of IP for a packet in order to avoid packet fragmentation.
Considering the MTU of  ethernet links (1500 bytes) a packet of 1200 bytes would not be fragmented even considering MPLS headers.
The departure rate is one hundred packets per second
In all scenario we will show how different protocols react to a link or node failure. 
The faults generation (and the eventual recovery of a link or a node) is possible in OPNET through the component Failure Recovery.
In order to enable OSPF we had to:

\begin{enumerate}[I]
\item auto assign every interface an IP addres.
\item assign a loopback address to every router.
\item select OSPF as routing protocol (the default protocol is RIP).
\end{enumerate}

During the simulation we disabled the OSPF\_sym\_efficiency flag in global parameters of the simulation.
With the flag on we had quite an erratic behavior among different simulations.

\input{ospf}

\input{cspf}

\input{frr}

\FloatBarrier
\section{ MPLS and static LSP}
\graphicspath{{./figures/STATIC}}

In this last scenario we tried to test MPLS with static lsp.
We used MPLS STATIC links  and imposed a path from source to destination.
In this case we need to specify a strict path since no reservation protocol is used.
Although we were able to configure the scenario in such a way that traffic was coupled to the desired lsp, there were no outgoing traffic from the lsp itself.
This is definitely a curious behavior and obviously no traffic can reach the destination.
\pagebreak
\section{Conclusions}

As we expected the fast reroute mechanism is the fastest one.
CSPF can also achieve restoration in less than a millisecond but a backup path needs to be precomputed and signaled.
OSPF requires a few seconds in order to reconstruct the topology of the network and restore the traffic flow.
Unfortunately we could not test all the scenarios that we wanted due to OPNET limitations.

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